JPH0588512A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain an image forming method in which the number of power sources used for respective component means for forming an image is kept to the minimum and by which a device is made compact and the cost thereof is made low. CONSTITUTION:By impressing AC voltage or voltage obtained by superposing DC voltage on AC voltage on the conductive base substance 11 of a photosensitive body 1 and bringing a conductive or semiconductive inducing member 2 which is grounded into contact with the surface of the photosensitive body 1 or making it close to the surface, the surface of the photosensitive body 1 is electrostatically charged to be in a specified polarity. Then, image exposure, development and transfer are performed, and the surface of the photosensitive body 1 is cleaned by a conductive or semiconductive cleaning means 5 which is grounded or bias-induced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method using electrophotography.

[0002]

2. Description of the Related Art In a conventional image forming method, the surface of a photoconductor is uniformly charged to a specific polarity by corona discharge means, and then the charge on the photoconductor is selectively erased by imagewise exposure to form an electrostatic image. Is formed, and the developer is supplied to the photoconductor by the developer supplying body to which an appropriate developing bias is applied to develop the electrostatic image.

The conventional method using such corona discharge means requires a plurality of power source means such as an expensive high voltage source for corona discharge, a developing bias power source, and a transfer means power source. Therefore, it is difficult to provide a low-priced image forming apparatus.

Further, the device using corona discharge is easily affected by the use environment such as humidity and dust and has a problem in reliability. Moreover, since it emits ozone, it is toxic to humans and harmful to humans. I have a problem.

In order to solve these problems, an image forming method using a charging roller to which an external voltage is applied or a transfer roller to which an external voltage is applied has been proposed instead of the corona discharge means.

A conventionally known method of this type is to ground a conductive substrate of a photoconductor and to inject charges into the photoconductor by bringing a charging roller to which a DC bias voltage is applied into contact with the surface of the photoconductor. Then, the surface of the photoconductor is charged. Then, an image to be copied is exposed on the surface of the photoconductor to form an electrostatic image corresponding to the image on the photoconductor.
The electrostatic image is developed with toner carried by a developing sleeve connected to a suitable developing bias power supply. The developed toner image is transferred onto a transfer material such as paper by the action of a transfer roller to which a transfer bias voltage is applied.
Residues such as toner remaining on the surface of the photoconductor without being transferred are removed from the surface of the photoconductor by a cleaning brush to which an appropriate cleaning bias is applied.

Although such a method can solve the above-mentioned problem of ozone generation, it is difficult to uniformly charge the surface of the photoconductor, and the formed copy image has image unevenness. It still has the problem that it is easy to cause background fogging.

As one of the proposals for solving this problem, a method has been proposed in which a charging roller to which a pulsating voltage is applied is brought into contact with a grounded photoconductor to carry out charging (Japanese Patent Application Laid-Open No. 63-9233). No. JP-A-63-149668).

[0009]

This conventional method can reduce uneven charging on the surface of the photosensitive member, but requires a high voltage power source for each constituent means for forming an image. That is, a power source for the charging roller, a power source for the developing bias, a power source for the transfer roller, and a power source for the cleaning bias are required. Therefore, it has been difficult to provide an image forming method for an inexpensive and compact device by this conventional method.

Therefore, the present invention provides a novel image forming method which minimizes the number of power sources used for each constituent means for forming an image, thereby making the apparatus compact and inexpensive. The purpose is to provide.

[0011]

Therefore, in the image forming method according to the present invention, an AC voltage or a voltage obtained by superimposing a DC voltage on an AC voltage is applied to the conductive substrate of the photoconductor, and the surface of the photoconductor is The surface of the photoconductor is charged to a predetermined polarity by bringing a conductive or semi-conductive inducing member that is grounded into contact with or close to it, and then, after the image exposure, development, and transfer steps, the ground is placed in contact with the surface of the photoconductor. Alternatively, the surface of the photoconductor is cleaned by a conductive or semi-conductive cleaning member that is induced biased.

[0012]

As described above, when an AC voltage or a voltage obtained by superimposing a DC voltage on an AC voltage is applied to the conductive substrate of the photoconductor and the inducing member is brought into contact with or close to the surface of the photoconductor, the photoconductive layer is applied according to the applied voltage. A charge of a predetermined polarity is induced on the surface, and the surface of the photoconductor is uniformly charged. Next, image exposure is performed to form an electrostatic image corresponding to the image information. On the other hand, electric potential is applied to the cleaning member by the electric potential applied to the photoconductor to establish a bias for necessary cleaning. The required value of this bias can be arbitrarily set by the rated value of a varistor or the like connected to the cleaning member.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming method according to the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an apparatus for carrying out an image forming method according to the present invention. The photoconductor 1 includes a drum-shaped conductive base 11 and a photoconductive layer 12 provided on the base 11 by vapor deposition or coating, and rotates in a direction indicated by an arrow A. The photoconductive layer 12 is OPC, S
Any type of P-type semiconductor or N-type semiconductor such as e, ZnO, CdS, and a-Si is suitable for use. Further, in addition to the above structure, a structure in which a dielectric layer is further provided on the photoconductive layer 12 may be used. The conductive substrate 11 of the photoconductor is electrically connected to the bias power source 6, and in this example, the bias power source 6 applies a voltage obtained by superimposing a DC voltage on an AC voltage to the conductive substrate 11. AC voltage is 80Hz-20KH
Those with frequencies in the z range are particularly suitable. In addition, the superimposed DC voltage is positive for the N-type photosensitive member, P
A negative voltage is preferably applied to the photoconductor of the type.

The inducing member 2 is arranged in contact with the surface of the photoconductor 1 (it is not always necessary to make strict contact depending on the case). In the illustrated example, the inducing member 2 has a roller shape in which an electrically conductive metal core 21 rotatably supported is covered with a layer 22 made of an electrically conductive elastic rubber material and is pressed against the surface of the photoconductor by an appropriate pressure. , Rotates in the forward direction at almost the same peripheral speed as the peripheral speed of the photoconductor. The inducing member 2 may be provided with a dielectric layer 23 (FIG. 4) made of synthetic resin or the like on the outer peripheral surface thereof in some cases. In addition to the elastic conductive material, the layer 22 is made of a semiconductive material (for example, 10 ⁵ to 10 ^10).
Ωcm) or a rigid metal body. The core 21 is grounded directly or through a rectifier such as a varistor, a constant voltage diode or a diode. Further, an appropriate resistor may be interposed in order to obtain a desired potential on the photoconductor. Further, the inducing member 2 may be in the shape of a conductive blade or brush other than the roller shape as described above.

FIG. 2 is an equivalent circuit for explaining the charging of the photoconductor. In the dark, the conductive substrate 11 of the photoconductor 1
When a bias voltage having a predetermined value in which alternating current is superimposed on alternating current is applied to the induction member 2 and the induction member 2 is brought into contact with or close to the surface of the photoreceptor,
The voltage is divided according to the values of the impedance of the photoconductor 1 and the impedance of the inducing member 2, and charges corresponding to the divided value are induced on the surface of the photoconductor. FIG. 3 schematically shows changes in the surface potential of the photoconductor when a positive potential is applied to the substrate of the photoconductor having the N-type photoconductive layer. Negative charges are induced on the surface of the photoconductor that is in contact with the induction member 2, and the potential drops according to the partial pressure. Next, when image exposure 7 is performed by an optical means such as a laser or an LED, the surface potential ( _VL ) of the image bright area (exposed area) approaches the value of the potential applied to the base 11 of the photoconductor, and the image dark area is exposed. A potential difference is formed with the potential (V _D ) of the (non-exposed region). Thus, in the electrophotographic method according to the present invention, contrary to the conventional method using corona discharge, an electrostatic image is formed in which the potential of the image bright portion is higher than the potential of the image dark portion.

Similarly, when a negative potential is applied to the base of the photoconductor having a P-type photoconductive layer, positive potential charges are induced on the photoconductor surface, and an electrostatic image is formed in the same manner as described above.

The electrostatic image is developed by the developing means 3 arranged next to each other. The developing means 3 includes a conductive sleeve 31 arranged close to the surface of the photoconductor 1 and a magnet roller 32 provided inside thereof. The sleeve 31 and the magnet roller 32 are rotatably provided independently of each other at different speeds. In this example, both the sleeve 31 and the magnet roller 32 rotate in the direction opposite to the rotation direction of the photoconductor 1. The developer supplied from a storage case (not shown) is attracted to the surface of the sleeve 31 by the magnetic force of the magnet roller 32. The developer is at the same speed as the peripheral speed of the photoconductor or at a speed slightly higher than the peripheral speed of the photoconductor 1 in the direction opposite to the rotation direction of the photoconductor 1 (direction of arrow B)
Then, the surface of the photoconductor 1 is rubbed to develop an electrostatic image. As the developer, a one-component magnetic toner or a two-component developer is used.

The sleeve 31 is grounded directly or through an inductive bias means such as a constant voltage diode, a high resistor or a varistor. In the illustrated example, the sleeve 31 is grounded via the constant voltage diode 33, and develops the electrostatic image on the photoconductor by the bias potential induced by the potential applied to the photoconductor drum. The bias potential of the sleeve 31 depends on the rated value of the inductive bias means such as a constant voltage diode or a varistor connected to it. For example, when reversal development is required as in a digital printer, the potential of the sleeve 31 becomes A rated value having a value close to the dark potential of the photoconductor is selected.

Then, the visualized developer image is transferred onto a transfer material such as paper by the transfer means 4. The transfer unit 4 has substantially the same structure as the inducing member 2, includes a grounded metal core 41 and a conductive layer 42, and in some cases, a dielectric layer 43.
(FIG. 4) is further included. The transfer unit 4 transfers the developer image on the photoconductor onto the transfer material by the transfer potential induced by the bias voltage applied to the photoconductor.

Then, the transfer material is separated from the surface of the photosensitive member by a separating means (not shown) and sent to a fixing means (not shown).
A permanent copy image is formed on it.

On the other hand, the photosensitive member after transfer is prepared for the next image formation by cleaning the developer remaining on the photosensitive member by the cleaning means 5. In this example, the cleaning means 5 comprises a brush type cleaner in which a conductive brush is planted on a conductive base 51. The conductive substrate 51 is grounded,
As a result, the developer remaining on the photoconductor is electrostatically and physically attracted to the conductive brush and removed from the photoconductor.
The developer attached to the brush is removed by a scraper (not shown).

FIG. 4 shows a case where the bias voltage applied to the conductive substrate of the photosensitive member 1 is only an AC voltage (no DC voltage is superposed). In this example, the inducing member 2 is grounded via the rectifying means 8. To be done. The other parts have the same configuration as the example of FIG.

Experimental Example 1 In the structure of FIG. 1, a photoreceptor having an N-type organic photoconductive layer on a conductive substrate has a frequency of 2 KHz and a voltage of 1500 V on the substrate.
A potential obtained by superimposing a DC voltage of +1000 V on the AC voltage of ^PP was applied, and the photoconductor was rotated at a peripheral speed of 40 mm / Sec.
An electrostatic image is formed by pressing a grounded induction roller having an elastic layer made of NBR or silicon rubber containing conductive powder against the photoconductor in the dark and then irradiating it with laser light. did. At this time, when the surface potential on the photoconductor was measured, the dark portion potential of the light image was + 280V and the light portion potential was + 1050V.

Next, a developing sleeve grounded via a constant voltage diode of a rating of 760 V is used to develop with a one-component magnetic developer having a positive polarity, and the developer image is transferred to a conductive and elastic transfer roller. When the image was transferred onto a transfer material with a la, and fixed, a clear copy image without fog was formed.

Experimental Example 2 The frequency of the AC voltage applied to the substrate of the photoconductor is 80 Hz to
When a similar experiment was performed by changing the frequency to 20 KHz and the other conditions being the same as those of Experimental Example 1, a clear copy image similar to that of Experimental Example 1 was formed.

Experimental Example 3 A bias voltage applied to the substrate of the photosensitive member was only an AC voltage, the inducing member was grounded via a varistor, and other conditions were the same as those in the experimental example. The image was formed.

Experimental Example 4 Under the conditions of Experimental Example 1, development was carried out using a two-component developer in which 5% to 45% of a carrier was mixed with a magnetic toner as a developer, and a very clear copy image was obtained. .. The magnetic toner used here was one containing 25% to 65% of ferrite powder.

[0028]

As described above, according to the present invention, an expensive high-voltage power source is not required, and the construction of the apparatus to be implemented can be made extremely simple and inexpensive. Further, by using an AC voltage or a voltage obtained by superimposing a DC voltage on the AC voltage as the bias voltage, a clear image without fog can be obtained. Further, the device can be simplified by similarly inducing electric charges to the cleaning member to perform the respective actions.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a main part of an example of an image forming apparatus that implements a method according to the present invention.

FIG. 2 is an equivalent circuit of a photoconductor and an induction member.

FIG. 3 is a diagram illustrating changes in the surface potential of a photoconductor when a positive potential is applied to the base of the photoconductor having an N-type photoconductive layer according to the present invention.

FIG. 4 is a schematic view showing an example different from FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Inducing member 3 Developing means 4 Transfer means 5 Cleaning means 6 Bias power source 11 Conductive substrate 12 Photoconductive layer 31 Developer supply body

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G03G 15/16 7818-2H 21/00 112 6605-2H

Claims (1)

[Claims] 1. An AC voltage or a voltage obtained by superimposing a DC voltage on an AC voltage is applied to a conductive substrate of a photoconductor, and a grounded conductive or semiconductive inducing member is brought into contact with or in proximity to the photoconductor surface. To charge the surface of the photoconductor to a predetermined polarity, and then, after the image exposure, development, and transfer steps, by a conductive or semiconductive cleaning member that is placed in contact with the photoconductor surface and is grounded or induced biased. An image forming method comprising cleaning the surface of a photoconductor.